Sexual Reproduction in Plants

1. Sexual Reproduction in Plants

2. Sexual Reproduction in Plants • Plants, like animals, can reproduce sexually. The same basic sequence applies to plant sexual reproduction as to sexual reproduction in animals. • Gamete formation, • Fertilization and zygote formation • Embryo development and growth of organism.

3. I’m not an angiosperm……and I’m not a gymnosperm… Then you must be a fern or a moss! These types of plants reproduce sexually, but don’t produce seeds……..in the case of ferns, spores are produced.

4. Flowers Sepals protect flower in bud Petals brightly coloured to attract pollinators

5. The parts of a flower

7. Pollination When a pollen grain reaches the stigma, it germinates and sends a pollen tube down the style. The pollen uses the sticky stigma as a food source. The pollen grain divides by mitosis forming 2 sperm. These, along with the pollen tube, travel down the pollen tube and grows through the style, the micropyle, and into the ovule chamber. The pollen tube with its contents makes up the mature male gametophyte generation.

8. Pollination problems to overcome • Pollination is the transfer of pollen (containing sperm) from one flower to a second.Since plants can not move, and sperm in flowering plants is not motile (no flagella), sperm transfer requires a pollinating agent. This dependency poses some problems for the typical plant: • You must attract an agent • You must have adequate pollen for transfer • You must convince the agent to take your pollen to another flower of your species (usually by providing a reward) • In fact, you want to be so special that the pollinating agent will visit your species exclusively, for at least the time that you are in flower. (Because pollen production takes energy, which should be conserved when possible.)

9. Cross vs Self Pollination Avoidance of self pollination is desirable because cross pollination results in more variation Methods to avoid self-pollination: Stamens and stigmas mature at different times Separate male and female plants(monoecious) Biochemical incompatiability Structual feature where insects directed past stigma before the stamens

10. Double fertilisation • Fertilisation involves the fusion of male and female gametes. • The pollen tube enters the ovule through the micropyle and ruptures. • One sperm fuses with the egg to form the diploid zygote. • The other sperm nucleus fuses with the polar nuclei forming the endosperm (the nutritive tissue). • Most angiosperms have mechanisms to avoid self-fertilization

11. Seeds • After double fertilization, each ovule develops into a seed, which consists of: • Plumule, made up of two embryonic leaves, which will become the first true leaves of the seedling, and a terminal (apical) bud. • One or two cotyledons which store food that will be used by the germinating seedling.monocotyledons. Examples: corn and other grasses. • dicotyedons. Examples: beans, squashes, • 3. The hypocotyl and radicle, which will grow into the part of the stem and primary root respectively. • The seed is a dormant embryo sporophyte with stored food and protective coats. • Its two functions: • Dispersal of the species to new locations (aided in angiosperms by the fruit) • Survival of the species during unfavorable climatic periods (e.g.winter).

12. Dicotyledon seed

13. Monocotyeldon seed

15. Fruits • Fruits are a development of the ovary wall and sometimes other flower parts as well. Fruits promote the dispersal of their content of seeds in a variety of ways. • Wind. The maple "key" and dandelion parachute are examples. • Water. Many aquatic angiosperms and shore dwellers (e.g., the coconut palm) have floating fruits that are carried by water currents to new locations. • Hitchhikers. The cocklebur and sticktights achieve dispersal of their seeds by sticking to the coat (or clothing) of a passing animal. • Edible fruits. Nuts and berries entice animals to eat them. Buried and forgotten (nuts) or passing through their g.i. tract unharmed (berries), the seeds may end up some distance away from the parent plant. • Mechanical. Some fruits, as they dry, open explosively expelling their seeds. The pods of many legumes (e.g., wisteria) do this.